(1) Field of the Invention
The present invention relates generally to ladders. More particularly, the present invention relates to ladders having mounting mechanisms configured for mounting the ladders to truck trailers for facilitating ingress to and egress from the interior of the truck trailers. Specifically, the present invention relates to a ladder mounting system having at least one moveable locking member that is adapted for locking engagement with the conventional door latching hardware, which is already present on conventional truck trailers for latching the doors thereof.
(2) Background of the Invention
In general, conventional truck trailers have an elongated, substantially horizontal cargo bed that is elevated four or five feet off of the ground. Commercial truck drivers often find it necessary to enter the elevated cargo bed of the truck trailers to load or unload cargo, to perform an inventory check, or to check the condition of the cargo or the trailer. This presents a significant risk of injury to the truck driver or other person attempting to enter or exit the cargo bed because it is necessary for the drivers to lift themselves up four or five feet to the elevated cargo bed by hand and to descend by jumping to the ground.
To reduce the risk of injury, a variety of devices have been developed to facilitate safe ingress to and egress from the elevated cargo bed of a truck trailer. While these devices, if used properly, provide a comparatively safer means of entering and exiting elevated cargo beds, they do have their limitations.
A problem with many prior art truck ladders is that they are difficult and time consuming to install and remove. Many are heavy and cumbersome, making them difficult to handle by one person. Some prior art ladders require mechanical fasteners and tools for mounting the ladders to the trailers. If such devices require more than a few seconds or require any type of tools for installation, the truck drivers may elect not to install the ladders and instead simply climb up by hand, thereby subjecting themselves to the risk of injury discussed above. Therefore, to encourage use of these devices, the devices should be relatively lightweight, so that they can be easily handled by one person, and they should be mountable to the truck trailers in only a few seconds, without the need for tools or any complex manipulations.
Other prior art truck ladders have been developed which are easier and less time consuming to install. For example, ladders have been developed having hooks with a generally inverted-U shape configured to fit over a portion of the horizontal sill extending along the lower edge of the doorway of the trailer. Thus, such ladders can simply be suspended from the sill with the ladder extending generally vertically over the ground. While such ladders are relatively easy to mount, they are unstable and tend to swing inwardly toward the front of the trailer when in use. Also, vertically disposed ladders are difficult to use when exiting the vehicle. Consequently, drivers using such ladders are subjected to many of the same risks of injury discussed above.
Thus, there is a need for a ladder mounting system for quickly mounting a relatively lightweight ladder to a truck trailer, without the need for tools or any complex manipulations, in a manner so that the ladder is secure and safely stable.
Conventional truck trailers have at least one door for closing the cargo storage area. Large semi-truck trailers typically have a pair of large rectangular doors that pivot between open and closed positions about vertical hinges. Such doors are commonly fitted with door latching hardware referred to as cam lock rods. U.S. Pat. No. 4,844,523 to Pastva (issued Jul. 4, 1989) discloses door-latching hardware of the general type that is in common use today. Door latching hardware of the type shown in Pastva is easy to operate and can be used by a single operator to tightly latch the doors at both the top and bottom with little effort. FIG. 1 shows a conventional truck trailer having a cam lock latching mechanism of the type disclosed in Pastva. As shown in FIG. 1, each cam lock device typically consists of a long rod attached to the outside of a vertically-hinged door at several points with pillow block type bearings, which allow the rod to rotate and move axially relative to the door. The ends of the rod extend beyond the upper and lower edges of the door, and each end includes a hooked locking member sometimes referred to as a "cam lock." Keeper members for receiving the cam locks are securely attached to the lower sill and upper doorframe of the trailer. The keeper members are positioned so that the cam locks can be easily inserted into the keeper members as the door is swung toward its closed position about its vertical hinges. The rod includes a handle for rotating the rod relative the door for bringing the cam locks into locking engagement with the keeper members to latch the door in its closed position. A beneficial feature of the cam lock rod hardware is that, at the point where a hinged door is nearly closed, the combined mechanical advantage of the handle, functioning as a lever, and the cam locks at the ends of the rod, make it relatively easy to securely close the door, despite any misalignment of the door or other frictional resistance. The door is unlatched by simply rotating the handle in the opposite direction to disengage the cam locks from the keeper members.
Other conventional truck trailers have slidable closures, such as overhead "roll-down" doors. Such doors are adapted for single hand operation in opening and closing and include a latching hardware that can also be operated with one hand. U.S. Pat. No. 3,622,189 to Rosehitz et al. (issued Nov. 23, 1971) discloses the latching hardware that is commonly used with such overhead doors, and which is still in common use today. The latching hardware comprises a hand lever pivotally mounted to the door and a keeper member, more particularly a "keeper post," recessed in the sill of the truck floor. Connected to the hand lever is a hook arm, which is biased by a resilient compression spring into engagement with the keeper post for latching the door in its closed position. The door is unlatched by simply rotating the handle in the opposite direction to disengage the hook from the keeper post.
The keeper members used with cam lock rods of the type disclosed in Pastva and the keeper posts of the type disclosed in Rosehitz are, by necessity, securely attached to the sill or door frame of the truck trailer. With the pressing need for safe truck ladders that can be securely mounted without complicated mounting hardware, these existing keeper members provide an excellent opportunity for use not only in latching the trailer doors, but also as components of a novel ladder mounting system.